Due to the recent advances of digital television (DTV), deinterlacing plays an important role in standard conversion between interlaced and progressive video scanning formats. For an image display of size M×N, where M and N denote the number of scan lines and number of pixels in each scan line, respectively, in an interlaced video scanning format, the picture formed by the stack of all even scan line m=0, 2, 4, . . . , M−2 is called top field (or even field). Each even scan line of the top field is called existing scan line while its odd counterpart whose pixels do not exist is called missing scan line. In a similar fashion, the bottom field (or odd field) is formed by the stack of all odd scan lines m=1, 3, . . . , M−1 which are the existing scan lines in this case. These two fields are displayed in an alternating manner at different time instants to form a complete image on the display.
The object of deinterlacing is to convert each M/2×N field (either top or bottom field) to a complete M×N image by interpolating each pixel in the missing scan lines from its neighboring (above and below) existing scan lines. Let d (in pixel unit) denote the detected direction obtained by the edge direction detection process. Referring to the example in FIG. 3, an interpolation of the missing pixel ƒ[m,n] in the current field f (e.g., field 300) can be calculated by the simple directional linear interpolation 302 which can be expressed as:
                              f          ⁡                      [                          m              ,              n                        ]                          =                              1            2                    ⁢                      (                                          f                ⁡                                  [                                                            m                      -                      1                                        ,                                          n                      +                      d                                                        ]                                            +                              f                ⁡                                  [                                                            m                      +                      1                                        ,                                          n                      -                      d                                                        ]                                                      )                                              (        1        )            where m is the scan line number of the missing pixel, and n is the pixel number in the missing scan line.
In deinterlacing, conventional edge direction detection techniques typically misdetect when direction |d| is large (the very low angle direction). For example, in FIG. 5(b), the edge direction detector may detect the direction d=−3 (or less, i.e. −4, −5, . . . , depending on the chosen vector length in edge direction detector) even though the more suitable direction should be d=½ or 0 (vertical direction).